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Wetlands of the United States

Their Extent and Their Value To Waterfowl and Other Wildlife

Wetland Soils

The more we use each individual type of soil for the purpose for which it is best adapted, the richer our nation and the more contented its people will be. * * * A land resource undiminished by repeated use represents the best in soil conservation. --Louis A. Wolfanger [14].

Soils provide the physical setting for generation after generation of man, lower animals, and plants. Wetland soils--a conspicuous feature of that setting--in many cases can be "improved" for man, for cultivated plants, and for domestic animals, or they can be left in their natural wet condition for wild plants and wild creatures. Geographic variations in climate, landform, and native vegetation largely determine the nature of the soil and hence the nature of acceptable land uses.

Mallards taking off

It may prove helpful, then, to take a brief look at wetland soils from the point of view of these geographic variations. Since it goes without saying that all wetland environments have some inherent wildlife values, which in many cases can be enhanced through habitat development, most of this discussion centers around past agricultural use--and, in many cases, misuse. Some wet soils have proved to be excellent cropland after being drained. Others have been completely unsuited to that purpose and should never have been drained.

As experience is gained in the field of soil capabilities, estimates of undeveloped wetlands that are physically feasible to drain for agricultural use have become progressively lower. Perhaps the day is near when a combination of soil science and greater wildlife-value appreciation will result in the setting aside of more and more wetland sites for wildlife use.

Some pedologists look upon soil as predominantly mineral matter found in subaerial rather than subaquatic situations. If this definition is accepted, those high-organic materials that are formed essentially from aquatic vegetation are actually not soils at all. Rather, they serve as the parent material from which future soils will develop. For soil-classification purposes, however, mineral soils are usually differentiated from the so-called organic soils associated with wetland environments.

Most types of waterlogged soils are grouped in two suborders known as hydromorphic and halomorphic. Hydromorphic soils are found in association with fresh-water marshes, swamps, seep areas, and flats. Halomorphic soils are the saline and alkali soils of imperfectly drained arid regions and the coastal salt flats of the humid belt. Alluvial soils underlie the remaining wetlands. Aside from alluvial areas and those upland depressions where water collects only for temporary periods, most wetlands delineated in this inventory are underlain by soil material known as peat or muck.


The U. S. Department of Agriculture Soil Survey Manual describes the formation and nature of peat and muck as follows:

In moist situations where organic matter forms more rapidly than it decomposes, peat deposits are formed. These peats become, in turn, parent material for soils. If the organic remains are sufficiently fresh and intact to permit identification of plant forms, the material is regarded as peat. If, on the other hand, the peat has undergone sufficient decomposition to make recognition of the plant parts impossible, the decomposed material is called muck. Generally speaking, muck has a higher mineral or ash content than peat, because in the process of decomposition the ash that was in the vegetation accumulates. [12]
Peat and muck cover a total area in the United States estimated at 79 million acres [11]. They exist under a wide range of climate and vegetation, but the most extensive areas are in the Atlantic and Gulf Coast marshes, Southeastern Coastal Plain, New England, the Great Lakes States, the Pacific Northwest, and the Pacific Coastal Valley Areas.

Northern areas. -- Northern peats and mucks are found in a cool-temperate, humid region extending from northeastern Maine and northwestern New Jersey to Minnesota and Illinois.3 They are also found scattered through northern Idaho and northern and western Washington on pitted plains, in stream valleys, and along borders of lakes. Native vegetation includes swamp forests of spruce, tamarack, and arborvitae in the north, and various conifers, maple, elm, and ash further south; reeds and sedges; and sphagnum moss and heath shrubs.

Peatlands in the northern sections of the region are not usually regarded as favorable for cultivated crops. They have not reached the advanced stage of decomposition of peat areas further south and are subject to late spring and early fall frosts. Many attempts at drainage have turned out to be expensive failures because the peat went through a period of shrinkage, and winds picked up the dry, fluffy particles from fields unprotected by windbreaks. This dry organic matter burns readily, and smoldering fires have destroyed many tons [14]. However, some of the drained, dark-brown or black granular muck soils in the southern part of this area have produced fairly good vegetable crops.

Southeastern Coastal Plain. -- Extensive areas of woody and fibrous peat and muck occur in the flat seaward part of the southeastern Atlantic Coastal Plain. They occupy level upland terraces and border practically all lakes and streams near sea level. This region has abundant rainfall and high temperatures that favor peat decomposition. Native vegetation is mainly cypress and tupelogum forests, and cane.

The most common types of fibrous peat are derived from underground stems and roots of former stands of cane, sedges, rushes, and grasses accumulated in water basins or on land with a rising water table. There are also large areas of woody-fibrous peat, known as pocosins, which developed from a mixed open growth of cane and sedges interspersed with shrubs, such as gallberry and waxmyrtle.

There is little agricultural development of the organic soils in this region, and there is little probability of extensive use in the future. Growing of timber and utilization as a hunting and fishing area are among the more permanent uses of these lands. In areas such as the Dismal Swamp of Virginia and the Okefenokee Swamp in Georgia, the layers of woody peat have retarded the flow of surface waters with the result that the waters have been impounded in natural lakes.

Gulf Coastal Plain. -- Peat and muck areas in the warm and humid Gulf Coastal Plain are typified by the Everglades of Florida. Some marshes enclose water basins, others border ponds and wooded streams, and still others are built up on sandy plains or on bedrock near sea level. The climate is subtropical and humid, rainfall is heavy, and plants grow luxuriantly. Marshes are characterized by tall sedges, grasses, and rushes. Cypress and tupelo gum are predominant in the swamp forests.

Good-quality muck has developed in a narrow belt bordering the southern shore of Lake Okeechobee, where sugarcane and vegetables such as onions, cabbages, tomatoes, peppers, and beans are grown.

Throughout many centuries the layers of peat along the northern border of the Everglades impounded waters from the Kissimmee River basin, gradually giving rise to Lake Okeechobee. Plans are now under way to devote a large part of the Everglades to water conservation and wildlife management. These projects would help conserve surface waters, replenish ground water and artesian wells, and provide an increasing army of sportsmen with a good place to hunt and fish--all of which are essential to Florida's great tourist industry.

Pacific Coastal Valley areas. -- In the semiarid Pacific valleys, peat and muck developed in the marshes of the Klamath Plateau of northern California and southern Oregon and in the delta lands at the confluence of the San Joaquin and Sacramento Rivers--about 50 miles inland from San Francisco. Rainfall is low, and summers are hot. Native vegetation is (or was) mostly reeds, sedges, rushes, and aquatic plants typical of shallow-water areas.

Drainage has been extensive in these two regions. At first, some of the drained areas under cultivation and irrigation in the Klamath district produced good yields of alsike clover, rye, barley, and tame grasses, but yields eventually declined as evaporation lowered the ground-water level and salts in injurious quantities accumulated at the surface.

The delta areas of California originally consisted of a number of peat islands. At present, most of these islands are under cultivation and are protected from overflow by levees. Yields are good to poor, depending on the type of peat. Under virgin conditions, the surface elevation of the peat islands was approximately at sea level. Since reclamation, most of them have been subsiding, and in some places cultural practices and occasional fires have lowered the present land surface to 8 or 10 feet below sea level.

In these inland areas of the Pacific slope, about 100,000 acres of drained but unproductive peat areas are now administered by the U. S. Fish and Wildlife Service for use by waterfowl. Most of the original wet conditions have been restored, and these areas now make excellent waterfowl refuges.

Coastal marshlands. -- Coastal marshlands occur mostly in tidal channels at the mouths of rivers, in quiet waters of lagoons, and behind barrier islands. There are about 9 million acres of these marshes, most of them along the Atlantic and Gulf coasts. They vary from highly saline to fresh, and their vegetation varies accordingly. It includes cordgrasses, saltgrass, bulrushes, spikerushes, cattails, and some shrubs.

Several types of peat occur, each with distinct characteristics and suitabilities for agriculture. Generally, the surface materials consist of coarse, fibrous, yellowish-brown peat, which has gradually accumulated over black, clayey mud flats or loose, gray sand.

Experience, both in this country and abroad, shows that some types of coastal marshes, when drained and used for hay or grain crops, undergo decomposition and a long-continued shrinkage. Ditches become more and more ineffective, and further drainage can be accomplished only through an increased use of pumps and dikes.


Alluvial soils occur in all parts of the United States on flood plains, first bottoms, or low terraces along rivers. They are composed of the recently deposited water-borne materials that are little changed by their new environment.

Some of the most productive soils of the world are alluvial in origin. Since they need protection from high-water stages of rivers, many areas are provided with levees and major drainage facilities which greatly reduce their wildlife value.

Alluvial soils of the Northeast, the Prairies and Great Plains, and the arid West are now largely under controlled management for agriculture. Row crops are grown on the better soils, and land that is still poorly drained is used for hay and pasture.

The largest area of alluvial soils in the United States is along the Mississippi River below the mouth of the Ohio. Flood-control and drainage projects have reclaimed much of this area for agricultural use, but millions of acres still remain unprotected from overflow--much of it is forested with oak, hickory, gum, ash, and cypress. Such areas are heavily used by migrating and wintering waterfowl, because overflow periods and availability of mast crops usually coincide with the seasonal movement of ducks.

Since 1880, approximately 8 million acres of agricultural land have been developed for farming in the 75 counties of the lower Mississippi Delta. Most of this development was preceded by drainage, but protection from floods was influential in stimulating land development [16]. This trend can be expected to continue in the future. Recent estimates indicate that nearly 6 million acres of fertile but undeveloped alluvial lands in Louisiana, Mississippi, and Arkansas are physically suitable, with improvements, for crop production and pasture [16].


Interior wetland soils suitable for future agricultural development are often in the areas that are used most heavily by waterfowl and other wildlife. Landform and native vegetation, singly or in combination, are probably responsible for this seemingly direct relation. Except for the alluvial valleys of the South, the best waterfowl wetlands are in grassland regions rather than forested regions, and where the relief is level to slightly rolling rather than strongly rolling or mountainous. The best agricultural lands also are found where such conditions are extant.

As an example, most of Minnesota's present-day drainage is in the flat to gently rolling grassland region of the State, where soils are inherently more fertile. This is also the region where most of the remaining wetlands are rated high in waterfowl value. High soil fertility and high wildlife production seem to go hand in hand where wetlands are concerned. This close tie-in between soil fertility and wildlife use has been noted for other game species--notably farm game and white-tailed deer.

Widespread drainage, of course, can upset this direct agriculture-waterfowl relation. Since the best agricultural lands are the ones receiving the most drainage, waterfowl habitat on such lands often becomes locally scarce. The birds are then forced to use less desirable locations. Population densities of breeding ducks in the Dakotas appear to be a case in point. The highest breeding-pair counts are recorded in the glaciated, hillier parts of the Dakotas, where drainage is uncommon.

The problem areas of the future are indicated in a general way in table 4. These estimates by the U. S. Soil Conservation Service [16] show the location, by States, of nearly 21 million acres of undeveloped wet soils that are considered physically feasible to drain and convert to cultivation. They include lands both inside and outside organized drainage enterprises. There is every indication that competition between agricultural and wildlife interests over the use of wetland soils will continue to be intense in the years ahead.

The current inventory by the Service and the States can furnish guidelines to show where the wildlife agencies should be prepared to go into action and where other land-use agencies need to lend a hand in a balanced program for dedicating wetland soils to their best permanent uses.

Table 4. -- Estimated acreage of fertile, undeveloped land that is physically feasible to provide with drainage in selected humid sections of the United States, 1948
[States excluded are Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, and Wyoming. Data from Wooten and Purcell, 1949]
Alabama683,000New Hampshire18,000
Arkansas1,865,000New Jersey60,000
Connecticut22,000New York100,000
Delaware34,000North Carolina1,157,000
Florida1,970,000North Dakota29,000
Kansas30,000Rhode Island4,000
Kentucky170,000South Carolina966,000
Louisiana2,769,000South Dakota88,000
Mississippi1,272,000West Virginia15,000

3This and subsequent descriptions of geographical areas are taken largely from the 1938 Yearbook of Agriculture.

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